Synthetic polymers, for instance, those based upon allyl resins such as diallyl glycol carbonate or polycarbonates, are used extensively for eyeglass lenses and other lenses in the optical industry. such polymeric lenses are advantageous since they can be manufactured inexpensively by casting or injection molding making it possible to obtain thereby complicated surface configurations directly without expensive grinding. While the diallyl glycol carbonates as a class of polymers are generally substantially resistant to abrasion and scratching as compared to polymethylmethacrylates, it is desirable to increase their abrasion resistance by applying thereto a hard transparent protective layer.
Field of the Invention
The invention relates to optical components such as ophthalmic lenses of synthetic polymer protected from abrasion by a coating of vitreous inorganic oxides.
Description of the Prior Art
Previous workers (German Pat. No. 1,204,048) in this art have sought to solve the problem of successfully applying a durable vitreous transparent protective layer to a synthetic polymer by applying a thin adhesive layer of Al.sub.2 O.sub.3 by vapor deposition and subsequently applying a protective layer of silicon dioxide by vapor deposition. Such compositions have met with adhesion difficulties in practice and the present invention provides an improved solution to the problem of protecting a synthetic thermoplastic polymer.
In U.S. Pat. No. 3,645,779 there is disclosed the protection of a diallyl glycol carbonate polymer substrate by the vacuum deposition of a glass in which the coefficient of expansion of the glass which is to provide a protective layer is adapted to that of the synthetic substrate by altering the proportion of boron oxide in the glass. The glass disclosed has as essential components boron oxide, silicon dioxide and up to 5% by weight of Na.sub.2 O. It has been found that such glass has a significantly lower thermal expansion than the plastic substrate. It has also been found that it is not enough to match the coefficient of expansion of the glass to that of the synthetic polymer to achieve a commercially satisfactory eyeglass lens since the coated lenses of the prior art remain sensitive to moisture in the air, as the diallyl glycol carbonate polymers are hydroscopic. As water is absorbed by the synthetic polymer, the bond between the polymer and the hard protective layer of the prior art is weakened ewith delamination eventually occurring. The present invention provides a solution to this problem by providing improved moisture resistance and adhesion of the glass coatings to the synthetic polymer eyeglass lens even without specific attempts to match the coefficients of thermal expansion of substrate and coating.
In U.S. Pat. No. 3,811,753 there is disclosed a coated optical component made of a synthetic polymer such as polycarbonate in which either silicon monoxide or silicon dioxide or both are deposited on the outside surface of the lens as a 1 micron to 10 microns thick vitreous coating consisting essentially of silicon monoxide and silicon dioxide. Deposition of the vitreous coating is by a conventional evaporation process. The vacuum evaporation process for forming a silicon dioxide film by vaporization of silicon monoxide in an oxygen atmosphere is disclosed in U.S. Pat. No. 3,248,256.
In Reissue No. 26,857 of U.S. Pat. No. 2,920,002 there is described a process for the manufacture of thin films of absorption-free silicon dioxide by the vaporization of silicon dioxide, preferably a mixture of SiO.sub.2 and Si in an atmosphere enriched with oxygen.
U.S. Pat. No. 3,700,487 discloses an anti-fog abrasion resistant coating of lightly cross-linked polyvinyl alcohol on a diallyl glycol carbonate lens in which adequate bonding of the anti-fog coating is obtained by first hydrolytically treating the polymer surface by dipping in an aqueous or alcoholic solution of caustic such as sodium or potassium hydroxide.